Logical switching system for input and output signals characterized by various stable frequencies



March 30, 1965 R. T. ADAMS ETAL LOGICAL SWITCHING SYSTEM FOR INPUT AND OUTPUT SIGNALS CHARACTERIZED BY VARIOUS mh s \mumm.

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March 30, 1965 R. T. ADAMS ETAL LOGICAL SWITCHING SYSTEM FOR INPUT AND OUTPUT SIGNALS CHARACTERIZED BY VARIOUS STABLE FREQUENCIES Filed Feb. 19, 1962 5 Sheets-Sheet 2 w m ad/ 2 I nkbo m m rm mm m w Q@ wm |l mim $5? ow H mw wm Gm n km o WSUQGQ 0.5 .\.u $335 G www .I m6 I REQ? .W u@ 2. QQ www mu .m @WONU m I @$52 m md QW 6M U Y W. NW m m6 m .vwvu Q m #www w w@ .i m ,m .Il m@ omg? m m6, wn s m u s@ .BUQ om Am nv U w eg I G 9 s s n@ Qwk ww" u@ G w INVENTORS.

RoaERr T. AOA/75 By BARRY M. M//vofs Mam@ ATTORNEY March 30, 1965 R. T. ADAMS ETAL 3,176,233 LOGICAL swTcHINU SYSTEM FOR INPUT AND OUTPUT SIGNALS CHARACTERIZED BY VARIOUS STABLE FREQUENCIES Filed Feb. 19, 1962 5 Sheets-Sheet I5 Y sm E M0 N Nm m Am T T TM A T Y A R 8 B mw March 30, 1965 R. T. ADAMS ETAI.

3,176,233 LOGICAL swITCHING SYSTEM FOR INPUT AND OUTPUT SIGNALS CHARAGTERIZED BY VARIOUS STABLE FREQUENCIES Filed Feb. 19, 1962 5 Sheets-Sheet 4 Mv o Y m 0 U wk QQYXQNQ Wk om m o A L NO ww m D W W o n A M w Vw U o N n u @G52 Q .QY k mx I M A M. v @n l f R Y L :u um um O OW R A m o e 0 U www T @EQ2 U .Q K mx v. ,um Dfw @m B mm, w o n U @G52 Qdi 0W @U mw \\\UQ mv uw. 0.x Qu wwwbww A W mm1. Qu?. r wok U o mv oi Si 200G AOOV Y wxw. Qovom .34T 6m NU u QQ wok NSUU O o T w ...k r R Nm TQM .um .um om uv m .Q uw Y um ok ox 1 ,www Qw .GN .X r .um A U @.@Sv n N T @Qllvm \U.\ o 9 "V GW W WW March 30, 1965 R. T. ADAMS ETAL LOGICAL SWITCHING SYSTEM FOR INPUT AND OUTPUT SIGNALS GHARACTERIZED BY VARIOUS STABLE FREQUENCIES Filed Feb. 19, 1962 5 Sheets-Sheet 5 Y .$5 nu M mMN m MAMMMW www. A l MR Y B United States Patent O LOGICAL SWITCHING SYSTEM FOR INPUT AND UTPUT SIGNAIS CHARACTERIZED BY VARI- OUS STABLE FREQUENCIES Robert T. Adams, Short Hills, and Barry M. Mindes, Fort Lee, NJ., assignors to International Telephone and Telegraph Corporation, Nutley, NJ., a corporation of Maryland Filed Feb. 19, 1962, Ser. No. 173,886 5 Claims. (Cl. 328-92) This invention relates generally to logical switching and selecting systems and particularly to a switching system wherein the only variable conditions are the frequencies of the input, control, and output signals.

There are many known systems for generating the basic logical switching functions of a plurality of variables, such as, for example, the functions of conjunction, disjunction and negation (AND, OR, and NOT). In the known systems, however, the varying signal parameter is either the signal amplitude, or phase. That is, the input and output signals are capable of assuming either a plurality of stable amplitude conditions, or a plurality of stable phase conditions. It is our discovery that a number of important system advantages accrue when switching or selecting circuits are designed to operate solely on signal frequencies, and the input and output signals are constrained to vary solely in frequency between a plurality of given stable frequency conditions. One such advantage is that, at very high frequencies, the design of wide-band switching circuits, in accordance with the inventiveprinciples to be enunciated below, is far simpler than the design of corresponding circuits for amplitude and/or phase switching. Further, the present invention affords a wide range of variation through a multiplicity of readily distinguishable stable conditions in contrast to prior-art noise-sensitive arrangements. Still further, in one particular aspect of this invention, a highly versatile switching circuit is provided as will be clear from the discussion given below.

It is therefore a general object of this invention to provide a logical switching system for producing output signals which vary in frequency between mn stable frequency states in accordance with a basic switching function of n variables each of which is capable of assuming m stable frequency states.

It is another object of this invention to provide a logical switching system in which a single basic circuit arrangement is capable of providing an output signal which varies through m possible stable frequency states in accordance with any one of a plurality of basic switching functions of n input variables each of which is capable of assuming m stable frequency states.

Another object is to provide a selection system for effectively coupling one of mn information input channels yto an output terminal, in accordance with the combined states of a plurality of selection control inputs, wherein the only variable aspect of the information input signals and the selection control input signals is that each signal is capable of assuming m different stable frequency states.

It is a specific object of this invention to provide a logical switching system in which a single basic circuit arrangement is capable of providing an output signal which varies between two stable frequency states in accordance with any one of sixteen possible basic switching functions of n input variables each of which is capable 'of assuming the same two stable frequency states associated with the output signal.

n According to one particular aspect of the present invention, a highly versatile switchingl arrangement has been devised which, in association with the combined condition of a plurality of variable-frequency control inputs is ca- 3,176,233 Patented Mar. 3o, i965 ice pable of providing an output signal frequency which varies as a corresponding predetermined switching function of a plurality of intelligence signal inputs. The same circuit arrangement is coincidentally useful for, in effect, selectively coupling one of the above mentioned control input signal frequencies to the output, in response to the combined frequency conditions of signals applied to the intelligence signal input channels. Thus, the circuit represents a highly versatile switching or selecting system arrangement.

These and other objects and features of the present invention may be more fully appreciated when considered in connection with the following description made in connection with the accompanying drawings, wherein:

FIG. l is a circuit block diagram characteristic of the basic arrangement of this invention as applied to two switching inputs exhibiting binary variable frequencies;

FIG. 2 is a circuit block diagram which illustrates exemplary frequency values suitable for use in the general arrangement of FIG. l, to provide the equivalent of an AND-circuit;

FIG. 3 is a circuit block diagram illustrating an exemplary set of values for producing an OR-circuit operation in the circuit of FIG. l;

FIG. 4 is a basic NOT-circuit illustrating an arrangement for producing the binary complement of an input signal in accordance with the invention;

FIG. 5 is a block diagram of a circuit arrangement employing the values given in connection with FIGS. 2-4, and illustrating the use of a' plurality of control signal sources each of which may be conditioned to the same stable binary frequency conditions associated with the input intelligence, and which are combined with the input intelligence in such a way as to provide, in effect, any one of the sixteen basic binary switching functions des fined in the table of FIG. 5A;

FIG. 6 is a circuit block diagram illustrating a method of providing all of the control signals required for the operation of the circuit of FIG. 5 from the two basic s tabli frequencies associated with the input and output signa s;

FIG. 7 is a general block diagram illustrating the general application of the present invention to the selection of one of m m-stable frequency signal inputs in association with n m-stable frequency selection inputs, or to the production of an m-stable frequency output signal related to n m-stable frequency inputs by any one of a multiplicity of switching functions associated with the combined conditions vof mn control inputs.

Referring to FIG. l, there is shown therein a general arrangement in accordance with the present invention for operating upon n input signals, each of which is capable of assuming m-stable frequency states, to produce an output signal, which is capable of ranging through the same m stable frequency states, in accordance with a predetermined switching function of the input variables. In the particular embodiment shown in FIG. l, both m and n are taken to be 2 so as to simplify the discussion, the extension of the description to general integers m and n being reserved for subsequent consideration below. Thus, in FIG. l, two sources S1 and S2, of input signals, which individually vary between two given stable frequency states, f1 and fo, are indicated. Sources such as the sources S1 and S2 designated in FIG. l which are capable of assuming two or more stable frequency states may for example comprise the well known multimode oscillators, which are shown and fully described in the IRE Transactions on Circuit Theory of March 1955, in an article on pp. 5 8-66, entitled Frequency Memory in Multimode Oscillators, by W. A; Edson.

. l, l Y ,2

In FIG. 1, the stable frequency conditions f1 and fo tions, as denoted by the respective (1) and .(0) indications above and below the input leads. The yinput signals from source S1 and S2 are applied to respectivemixers 1 and 2 which are respectively supplied with control input signals C1 and C2' each of a given frequency'v andamplitude. The outputy of mixer 1 is coupled to'v frequencyselectivey circuit 3 'whichfserves .to selectively pass one i of the beat-frequency signalcomponents (either the sum may be'viewed as representative of binary 1 and 0 condiever, as will be'clear from the discussion of the NOT- circuit of FIG. 4 below, conversion of thev basic input frequencies -prior to application thereofV tofrequency selectivev channels, may Anot be necessary, in given in- VItis.thus'clear thatin the .basic arrangementiof FIG. Y1 the frequenciesof the input signals are firstY converted e and thereafter combined in a mixer so as to provide a or'diiference) produced by the. mixing Aof the signals S1 and C1'for each possible frequency state (f1 andY fo) of the signal S1. Thus, at the output of circuit .3, a signal of converted frequency f1? or for is obtained. depending respectively upon whether thefrequency of S1 1s f1 or fo. Similarly, the output of mixer 2 isfcoupled to a cir- Y cuit 4 which produces aksignal at a 'converted frequency f1 or fg, for S2 respectively equal to f1V or fo, the free'- quencies f1 and fo being distinct from each other and yfrom the frequencies f1and fo', as well as from rthe basic frequencies f1 and fo.

The outputs of circuits 3 and 4A are coupled to a mixing circuit S whichserves to produce oneY and only. one-of four possible composite signals, this compositesignal containing one and only one of Yfourdiderent frequency components which are thus uniquely determined by the combinations of thefrequencies of input signals S1 and S2. The output of mixer 5 is applied to four lilter. networks including frequency selective elements 6-'9 whichserve to extract the aforesaid four different frequencyy components from theV corresponding composite signals.. The frequencies/of the outputs ofthe filters 6-9 may thus be designated f11, f1.1, 101, and, fob, respectively, to indicate theircorrespondence to the fass'ociatedcombined states of the signals S1 and S2 as indicated in .parentheses next to the frequency designation. The indication NSl below the outputof each ilterfcircuit `69 represents the state no signal,V as the unique signalfconiponent at the output of mixer 5 is passed through one andonly oneV ofthe lters 6-9. i

'The outputs of vfilters 6-9 are respectively mixed Y composite signal including one and only one of vfour posis the same .as that of the inputs 'and it varies in accordance with the desired. switching function determined by 1 the control signals ,C2-C6.' VSuitable stable frequency valuesfor the 1 and 0 `states are, for example, 6.5 kmc.

and 5.5 kmc. (kmc. beingkused asV an abbrevartion for kilomegacycles), respectively. Under these conditions, appropriate values for the control signals C1 and C2 are respectivelyv2.5 kmc; and 1.5 kmc., so that Ithe corresponding Vvalues of the signals 11,j0, f1,;and f1, may, for example Ybe 9, 3, 8 and 7 kilomegacycles respectively. Accordingly, the four unique frequencies.-'associated with the frequency combinations.9'-8, 9-7, 348, and, 3-7, may for jexamplelbel kmc., 2-kme., 5 kmc., and 4 kmc., respecx tively, these ycorresponding respectively to the binary in-V put conditioncombinations.S1 S2 (11), S1 S2 (10), S1 S2 (01) andSfSZ (60).y VReferring to FIG. 2, ifthe above specific frequency vValues are'employed, it is clear that Y one and Vonlyv one ofthe filters 6a-9'a will pass a signal at any given time.

Further, if the signals' C3-C6 are respectively 7.5, 3.5, 0.5 and 1.5 kmc. Signals, as shown control signalsY C11-C6 in mixing circuits lil-13,V Sothat.

at any given time the output of one and only one of the circuits 10-13 Will include a frequency component atV either thev frequency f1, or.v the frequency fo, .depending uponthefrequired switching function. This output-iis passed through a corresponding one of thefreque'ncyf i. 51.5 kmc. for filters 15a-17a.

selective networks 14-17 to a common output 18 as an output signall S3, which is thusrepresentative of either a binary 1v or 0 condition depending vupon the associated passedv frequency component. Y.

f summarizing, it'may be ppreciated that thecircuits 1-*5 designated Yas a group within the dotted line block 19, serve to produce in response Vto thecombined 'fre-A quency conditions-of thesources S1 and S2an output signal including one and only oneof four different frequency lcomponents which correspond. lto the lfour possible com- Y bined states of the sources yS1 and S2; The associated, I

inFIG,v 2, then one and'only one of the mixers 10a-13a will provide an output frequencycomponentat one kof the basic Vstable input frequencies (in this'instance, 6.5 or 5.5 kmc.). Accordingly, filter circuits 14a-17a' are respectivelyy .coupled to mixing circuits 10a-43a to extract the'associated outputfrequency component which, for the indicated input values will be'6.5 kmc. for i1te`r'14a and In operation, therefore, wheny S1 and' S2 are both in the binary 1 condition.(6,5 kmc.), lter 6a passes a 1 kmc. .signal to mixer 10a which combines the. passed signal with a 7.5A kmc. control'signal C2 to produce a signal including a 6.5 lemc. component which is passed to the outl'put terminal 18a. For the other three possible input concomponentis thus passed through oneV and only one of the frequency selective channels V6-9 `to a'1n'associated`-or1eV of four mixing circuits 10-13 where it is mixed with an yassociated one 'of four .control signals C11-C6'V to produce a composite signal including a frequency/component at one of the binary stable input states f1 or fo. Thiscomp'onent is coupledthru a corresponding one of the. Vfour frequency-selective networks 124-17. toA output terminalv18 as the required output signal S2 whichV thus assumes4 the frequency states corresponding toy binary 1 and 0 condif tions in accordance with va binary `switching function of Y' the inputs S1 and S2y as determined bythe frequency vof the corresponding one of the control signals AC3 6.

- The mixers 1 and 2 are usually re'quiredtoensure Su'i- 'cient separation vin'fre'qu'ency between the fourr possible unique output frequency components of mixer.Y 5. HoW--.

condition).

ditionsV of .signals S1 and S2,'oneof the circuits 7a9a passes a signal"which,.when mixed withthe corresponding one `ofthe control signals VC.1,-C6',V yields .a composite signalatthe output of the associated one ofmixers 11a-13a. This `.compositev signal' includes a 5.5 kmc. component which will passthrough the associated .515 kmc. filter to the output. Thus, the output isr a 5.5 kmc. signal unless both inputs are 6,55 kmc. signals, and in the latter instance the output J-is a 6.5 kmc. signal (binaryl),f.and.therefore itis clear that the circuitry of FIG. 2 represents an AND- circuit. Y Y l. j Similarly, FIG.. 3 employing frequency values correspondingto those .shown in FIG. 2, with different-controlv signals CgaC represents anv OR-circuit; In FIG. 3, C11-C5 are assigned the vrespective frequency Jvalues 7.5,v 4.5, 1.5, and 1.5 kmc., and, the lternetworks 14a-'.

17a (of FlCneZ) are replaced by networks 1411-171; which respond respeetivelyto 6.5, v6.5, 6.5,'and 5.5 kmc.'signals. Thus, the output 18b isV always at`6.5 .kmc.y (binaryl) unless both ofthe inputs S1v and S2 are Iatf5.5 kmc. (OR- In FIG. 4, a `NOT-circuit is shown. As previously noted, this circuit is considerably simpler than the abovediscussed AND and OR circuit arrangements. Specifically, no frequency conversion is required prior to the insertion of the input signal into the associated one and only one of the frequency selective output channels. More specifically, in FIG. 4 the signal .at vthe input 25 is applied directly to frequency selective networks 26 and 2'7 without prior frequency conversion. Thereafter, the outputs of networks Z6 and 27 are respectively coupled through mixers 2S and 29 to frequency selective networks 341 and 31, respectively. The control signals C1 and C8 applied to the mixers 2S and 29 vare such as required to produce a unique one of the two possible input signal frequencies as a component .at the output. Again specifically, if the input signal S1n at terminal 25 is capable of assuming the frequency 6.5 kmc. or 5.5 kmc. depending upon whether it is in the binary l or condition, respectively, then for a binary 1 input, the circuit 26 will pass a 61.5 kmc. signal through mixer 28 which, when mixed with the 1.0 kmc. control input C7 results in a composite signal including a frequency component of 5.5 kmc. which is passed to the output terminal 32 as the required cornplementary binary 0 output. During the same interval of time, the channel including circuits 27, 29, and 31 remains relatively unenergized, since the output of mixer 29 does not include a 6.5 kmc. component. On the other hand, if the input assumes the state binary 0, a 5.5 kmc. signal is passed to mixer 29 where it is mixed with a 1.0 kmc. signal to provide `a composite signal including a 6.5 kmc. (binary 1) complementary frequency component as required, which component is passed through frequency selective network 31 to output terminal 32.

Referring to FIG. 5, one of the more important advantageous aspects of the present invention may now be appreciated by considering the arrangement shown therein in relation to any of the arrangements previously discussed. In FIG. 5, the upper half of the circuit including the frequency converting arrangement 19a, the frequency selective channels 132-961, and the associated mixers 10a-13a, respectively, are substantially identical to the corresponding elements considered in connection with the discussion of FIG. 2. What is different, however, is that the output frequency selective channels llt-17, which are now distinguished by the subscript c, are each capable of passing two signal frequency components corresponding to binary frequency conditions of the control inputs, C11-C6 which are each at one of two predetermined frequencies, rather than a constant frequency as implied throughout the previous discussions. The advantage of this is that the arrangement of FIG. now may be conditioned to provide at the output 18e a signal S3 which may represent any one of a plurality of different switching functions of the input signals S1 and S2.

r Considering the specific frequency values previously employed in the arrangements of FIGS. 2-4, the control signal C6 is derived from a control input signal X1 which assumes one of the two stable frequency states associated with the binary 1 and 0 conditions. Similarly, the control signal C5 is derived from a binary input X2, C1 is derived from a binary input X3, and C3 is derived from a binary input X4. The binary control inputs X1-X4 are coupled through respective delay networks 355-38 to corresponding mixers 39-42, where the output frequencies thereof are mixed with associated control signals C11-C12 having respective frequencies 4 kmc., 5 kmc., 2 kmc., and l kmc. which, it is incidentally noted, are identical to the respective frequencies transferred by the filters 9a, 8a, 7a, and 6a to the respective mixing networks 13a-10a.

The outputs of the mixing networks 39-42 are coupled to frequency selective networks 413-46 each of which thus passes one and only one of two possible frequency components to the corresponding control lead associated with the signals C11-C3. f Thus, if X1 is in the binary 1 condition, a 6.5 kmc. signal will pass through delay network 3S to mixer 39 where, after mixingwith the-4 kmc.

signal C2, the composite output includes a frequency.

component of 2.5 kmc. which is applied to the signalC to the mixer 13a. On the other hand, if X1 is in the 0 condition, then a 5.5 kmc. signal will pass through network to mixer 39, so that a 1.5 kmc. signal will be isolated by the network 43 and applied to mixer 13a. Similarly, if X2 is respectively in the 1 or 0 condition, C5 will respectively assume the frequency state 1.5 kmc. or 0.5 kmc., and if X3 is respectively in the 1 or 0 condition, C.1 will assume the frequency condition 4.5 kmc. or 3.5 kmc., and if X4 is in the respective 1 or 0 condition, then C3 will assume the condition 7.5 or 4.5 kmc., respectively. Since one and only one of the frequency selective networks naz-9a passes a signal at any given time, it may be appreciated that one and only one of the mixing circuits 10a-13a will produce an output which includes a frequency component within the range of the associated one of the frequency selective networks 14C-17C. More particularly, in view of the fact that C6 can only be at the frequency 2.5 or 1.5 kmc., the output of mixing network 13a will include a frequency cornponent at 6.5 or 5.5 kmc. only when circuit 9a passes a signal at frequency 4 kmc., the latter condition occurring only when both of the inputs S1 and S2 are in the binary 0 conditions. Similarly, it may be shown that a signal will be passed through network 16e only when the inputs S1 and S2 are in the binary 0 and 1 conditions, respectively, that network 15c will pass a signal only when inputs S1 and S2 are respectively in their binary 1 and 0 conditions, and that network 14e will pass a signal only when both of the inputs S1 and S2 are simultaneously in the binary 1 condition.

From the truth table given in FIG. 5, it may be appreciated that any one of the 16 basic binary switching functions of the inputs S1 and S2 is available at the output depending upon the combined conditions of the control inputs X1-X4. For example, the first row entry in the table indicates that if the control inputs X1-X4 are in the respective states 0001, the output S3 represents the switching functions S1.S2, where the dot indicates conjunction (read S1 AND 82). Again by way of example, if the entries in the second row of the table are inspected, it may be noted that if the input X1-X.1 assume the states 0111 coincidentally, the output S3 is related to the inputs by the following expression (read S1 GR S2). Further, if the control inputs are as shown in the fifth row entry of the table in the state 1100, the output will be 'S1 (read NGT 81). Thus, any one of the 16 basic switching functions may be produced at the output depending upon the state of the control inputs X1-X1.

The row entries in the table in FlG. 5a are identified by the function designations F1-F16 to permit convenient reference thereto. In connection with the entries F1, F9, F111, and F11 another advantageous aspect of the arrangement of FIG. 5 may be appreciated. It may be recalled that, depending upon the combined states of the inputs S1 and S2, one and only one of the networks 6a-9a will pass a signal which when mixed with the corresponding input to the associated one of the mixers 10a-13a will produce a signal having a frequency component in the range of the corresponding output frequency selective network. Accordingly, it may be appreciated that if, for example, the inputs are both in the state binary l, then regardless of the conditions of the control signals X1-X2, the output S3 will depend solely on the control signal X1. If X4 is in the condition binary 1, the output will also be in the condition binary .1 (6.5 kmc.), and so forth. Similarly from entry F9, it may be seen that if S1 and S2 are in the respective states 1 and 0, the output S3 will depend solely on the (control) input Xwlandwill berlin the conditionl orV l) depending respectively uponwhetherthe control input Xais in the,

1 or.Gvfrequencyfcondition. Thus, the combined states ofthe inputsy S14 and S2,'in effect, may be usedl to Vselectively. coupleone and only one ofthe eontrol'inputs X1-X4 to the output channel S3, and therefore Ythe circuit a, Weges;

-1 such llterlcircuit.blocks'beingindicatedv generally at 54,

`to produce an outputA which maybe vviewed either as a given multilevelswitching .function of Vthe inputs S1,

which hitherto has been considered as a switchingrfunction yarrangement may also be viewed as a selecting cir-y cuit arrangement. A Y l Y It isfurther noted that the delay lines 35-38 of FIG. 5 are only used to compensate forthe expected delays of the input signals S1 and S2 through the mixing circuitsV Y Vof the frequency conversion arrangement 19a, as itmay l be appreciated that at Vthe high kmc. frequencies in-` volved, any Vslight delay in passage of a signal through a cascaded vmixing network, can result `in an erroneous output. By Vproperly delaying the control signalsX1-VX4 S11V or,as` a selection'of the signal input XJ in response to an appropriatev selection combination of the vinputs. S1, v. Sn. The control signals XJ--are indicated as being passed through om parallel frequency-converting networks indicated generally ats55, the outputsof which are filtered through mn banks of parallel filter circuits each including m filter channels corresponding tothe assorelative to. the signals propagatingthrough the circuit 19a and the` associated channels ,6a-9a, the signals mixed in mixers 10a-13a may therefore be properly synchro-Y nized. Y

Referring to FIG. 6, an arrangement for deriving all ofthe control signals employedcin the. arrangement of Y FIG. 5 from the two basic signal'frequencies f1'and fo corresponding to the l and 0V conditions, respectivelyY r(6.5 kmc. and 5.5 kmc., for example), is shown.

Spe-Y ciically, it is noted lthat the control signals C11-C12 apciated converted frequency, the lilter banks being indicated generally at 56, thereby supplying lthe required mn control signal inputs to the mixing networks 53.

It should thus be clear that -the arrangements considered in connection with FIGS. 1-5 are adapted to a wide range f of applications within the 'contemplated scope, and acplied to the mixing circuits 39-42 ofFIG. 5 are derived Y from the outputs of the corresponding filter channels 9`a-6a, respectively.` Similarly, theoutputs ofthe frequency selective networks 3c and'4c, includedY within the4 frequency convertingrblock 191e, are shown as being cou` v f pled through respectively associatedmixing circuits 44 v and 45, where they-are respectively mixed with the input signals S1 and S2, and appliedrto frequency selective netfworks 46V and 47- which serve tov respectively fil-ter out c the required control frequency components'vC1rand C2. Thus, the control signals C1 and C2 maybe derived` directly from the basic input signals S1 andfSZ. f

Referring now to FIG. 7, thisYV illustrates the general applicability of the present arrangement, particularly thearrangementshown in'FIG. 5, yto the handling-of n input signals S1-Sn and mn control signals X1`Xmnfto produce an outputvwhich may be viewed as either the required switching function of the inputs S1-Sm or as a selected one ofthe signals X1-Xmnl in accordance with the combined conditionsof the signals S1-Sn, where the signals v l S1-Sn, X1-Xmn, and the output S out, are each capable of ranging through m stable frequency states. In FIG. 7, the extension of the circuit of FIG. 5 to handletleY general collection of inputs S1-S1 X1 Xmn` includesYV a block 50 which is coupled to the inputsY S1 ."L Sn and to corresponding control inputs C1 Cn. Each of the inputs S1, l. Sn is capable of assuming any one of m stablefrequency states indicated as`f1, f2,'. fm. The signals S1,

shown in the block 50, but which are `deemed obvious Yin view'of the discussion of the preceding figures, the

tracted by means of an appropriate one of mn parallel lter circuits indicated generally at 52, and the correj Sl1 are respectively mixedrwith the` signals C1, Cn to produce n composite signals at fre-Y quencies lso determinedY that when'mixed by means notV Sn. The aforementioned Y uniqueA signal component which Vis thus produced is ex-v a limitation to the scope of the invention as set forth in the objects thereof'and'in the accompanying claims.

Accordingly we claim: Y l. A logical AND-circuit comprising:

two sources ofinformationsignals each capable of assuming lirst and second stable frequency states correspondingrespectivelyto binary Ione and zero con- 1 ditions A l v 7 means coupled to saidk sources for producing a composite -signal Yincluding a predetermined signal component atone and only one of four given discrete .frequencies, in accordance with the-combined frequency states of saidisources, j Y

four frequency selective networks coupled yto saidlastmentionedY means for filteringV out associated ones of said predetermined signalcomponents,

four control signal-sources,l f

and means coupled to saidsfrequency rselective networks andY said control Asignalsources for'converting the frequencyvof said-filtered signal componentwhich is produced in response to the coincidentV presence of said first-stable frequency at-the outputs ofv both said v Y information signal sources, to said first stable' frequency, andcfor converting the frequencies vof all of Vsaid other filtered signal components to said second stable frequency. Y l

2. A log-ical OR-circuit comprising:

'Y two sources of information signals each capable of vassuming rst and :second stable'frequency- `states correspondingrespectively to binary one and zero Y Y four control signal sources,

sponding filter circuit output isv coupled to an associated Y one of mnlmixing networks indicated generally at 53 where the selected Vfilter output 'is mixed with a corref i sponding one of mn control signal inputs derived from aA Y corresponding one of mn (control)'signal inputs X1 Y, Y Xmn. The outputl of -the associated mixing network,-a nd` ronly that network,will then include asignal component and means coupled to saidfrequency selective networks l and said control signal sources for converting the VfrequencyofV said Vfiltered signal component, which is Yproduced in response tothe coincidentr presence of'said second stable' frequencyat the outputs of both `Vsaid'information signal sources,'to vsaid second stable frequencyfand.forrconverting the frequencies of all of Vsaidother filtered signal components to said first stable frequency', Y v- 3,. Arlogicalswitching', system comprising: Y

two sources o f information'signals each of which is capable of assuming two stable frequency states which are representative of digit intelligence referenced to the base two;

means coupled to said sources for producing an output signal at one and only one of four possible different frequencies and at an associated one of four output terminals, in accordance with the instantaneous combined frequency conditions of said sources;

four frequency-selective networks coupled to said four output terminals; and

means coupled to said frequency-selective networks for converting the outputs of said networks to predetermined ones of said base-two-referenced digit-representing stable frequencies associated with said sources, whereby the output of said last-mentioned means represents a predetermined switching function of the frequency conditions of said sources.

4. A logical switching system for selectively generating v any basic switching function of two binary variables comprising:

two sources of information signals each capable of assuming first and second stable frequency states corresponding respectively to binary one and zero conditions;

means coupled to said sources for producing a composite signal including a predetermined frequency component at one and only one of four different given frequencies;

four frequency-selective networks coupled to said lastmentioned means for filtering out associated ones of said four predetermined frequency components;

four control-signal sources each capable of being conditioned to said rst and second stable frequency states associated with said information-signal sources; and

means coupled to said frequency selective networks and said control-signal sources for converting the frequency of said filtered predetermined frequency component to a predetermined one of said first and second stable frequencies in accordance with a predetermined switching function of the combined frequency conditions of said four control signals, and for transferring all such converted signals to a common output channel.

5. A selection system for coupling signals at one of four input terminals to a common output terminal in accordance with the combined conditions of two selection inputs comprising:

four sources of information signals each capable of assuming two stable frequency states; two sources of selection-control signals each capable of assuming said two stable frequency states;

means coupled to said selection-control-signal sources for producing a composite signal including a predetermined frequency component at one and only one of four different frequencies associated in oneto-one fashion with the four possible combinations of frequency states of said two selection-controlsignal sources;

means coupled to said last-mentioned means for filtering said predetermined frequency component into a corresponding predetermined one of four signal channels; and

means coupled to said four information-signal sources and said four signal channels for producing an output signal at the stable frequency of said informationsignal source which is coupled to said predetermined signal channel.

References Cited by the Examiner UNTED STATES PATENTS ARTHUR GAUSS, Primary Examiner. 

3. A LOGICAL SWITCHING SYSTEM COMPRISING: TWO SOURCES OF INFORMATION SIGNALS EACH OF WHICH IS CAPABLE OF ASSUMING TWO STABLE FREQUENCY STATES WHICH ARE REPRESENTATIVE OF DIGIT INTELLIGENCE REFERENCED TO THE BASE TWO; MEANS COUPLED TO SAID SOURCES FOR PRODUCING AN OUTPUT SIGNAL AT ONE AND ONLY OF FOUR POSSIBLE DIFFERENT FREQUENCIES AND AT AN ASSOCIATED ONE OF FOUR OUTPUT TERMINALS, IN ACCORDANCE WITH THE INSTANTANEOUS COMBINED FREQUENCY CONDITIONS OF SAID SOURCES; FOUR FREQUENCY-SELECTIVE NETWORKS COUPLED TO SAID FOUR OUTPUT TERMINALS; AND MEANS COUPLED TO SAID FREQUENCY-SELECTIVE NETWORKS FOR CONVERTING THE OUTPUTS OF SAID NETWORKS TO PREDETERMINED ONES OF SAID BASE-TWO-REFERENCED DIGIT-REPRESENTING STABLE FREQUENCIES ASSOCIATED WITH SAID SOURCES, WHEREBY THE OUTPUT OF SAID LAST-MENTIONED MEANS REPRESENTS A PREDETERMINED SWITCHING FUNCTION OF THE FREQUENCY CONDITIONS OF SAID SOURCES. 